A number of types of implantable leads for use with a cardiac pacemaker and/or defibrillator to form a pacing system are known in the art. Some leads require transvenous insertion and have a portion of the lead body inserted into the vein and extending into the heart. The remainder of the lead body which is not inserted into the vein extends to a point of attachment to an implanted pacemaker. The leads generally include at least one electrode which is implanted at a particular location within the heart. The implant location is particularly critical in order to allow optimum system performance. Thus, it is imperative that the electrode, and thus the lead body, are securely positioned in order to prevent dislodging of the implanted electrode after implantation.
Accordingly, it is common to utilize a suture sleeve, located about a portion of the lead body, which is secured to tissue in such a manner that the potential for displacement of the lead body is minimized. Generally, the suture sleeve is positioned proximate the point of venous insertion. Various types of suture sleeves have been used in the art, including sleeves which are integrally formed with the lead body and thus stationary in their location, and suture sleeves which can be slidably positioned axially along at least a limited portion of the length of the lead body. The primary advantage of the suture sleeves which may be slidably positioned along the lead body is that the lead may be implanted in patients having a range of physical dimensions, and the suture sleeve may be positioned appropriately.
Generally, the suture sleeve is positioned proximate the point of venous insertion and secured to the lead body using suture material and a suture tie. The suture sleeve is then secured to the surrounding tissue using a suture needle and suture thread. The suture sleeve preferably includes a slot which allows the attending physician to wrap the suture thread around and over the suture sleeve a number of times, each time securing the thread to the adjacent tissue.
A recurring problem with the use of suture sleeves to secure the lead body results from the potential for the attending physician to overtighten the suture thread about the suture sleeve, thereby crushing the electrical conductors or insulation extending through the lead body. For most lead body applications, the electrical conductors extending between the proximal and distal ends are formed into a helix defining a central open core. The benefit of the helical conductors is that the lead body is highly flexible yet durable. The disadvantage which results is the potential for flattening or crushing of the helix, thereby incurring localized stresses within the conductors which may cause parting of the conductors or breakage of insulation resulting in failure of the lead.
Accordingly, it would be desirable to have a suture sleeve which is both adjustable along a portion of the length of the lead body but which prevents or minimizes the risk of damage to the electrical conductors or insulation of the lead caused by overtightened anchoring sutures. While the adjustable feature of the suture sleeve is desirable, the suture sleeve should also be designed to secure the axial location of the lead body once the position of the suture sleeve is fixed. Suture sleeves of the prior art which are slidably positionable yet structurally rigid enough to prevent the suture threads from damaging the conductors are not easily secured to the lead body.